Glass units made from two, and sometimes more, panes of glass are well known. They are particularly used as insulating glass units where the two panes, or lights, of glass are sealed together in spaced apart relation. Spacers separate the two lights, and are affixed to the respective lights around the entire perimeter of the combined lights. The lights are thus sturdily secured into a unit with an air or other gas layer typically trapped between the two lights, establishing the insulative character of the unit.
Fairly large glass units may be used on office buildings and the like, such as glass units running from floor to ceiling. A number of different techniques have been developed to attach such glass units to a building. One method, for instance, is to attach the glass unit using end caps or exterior stops. The end caps or stops overlie the outside light of the unit and are anchored or clamped to the building. Such a mounting mechanism is shown in U.S. Pat. No. 3,367,077 for example, although a double-paned unit is not described therein.
While the foregoing method provides a very good attachment of the glass unit to the building, many buildings call for mounting the units without the use of exterior stops or caps. One common way to accomplish this is to adhere the interior light of the unit directly to the building. This can either be done in the field, or by adhering the unit to a frame remote from the job and then attaching the frame in place on the building (commonly referred to as unitization). In either case, the structural adherent used would ordinarily be a one or two part silicone sealant, preferably one that cures rapidly. The sealant is applied around the entire periphery of each unit to further weather-seal the unit to the building.
It will of course be readily appreciated that the entire weight of the unit is borne by the sealant. Wind forces are also directly borne by the sealant, as are stretching forces imposed by the expansion and contraction of the interior light. If the sealant fails, which unfortunately does occur, the entire unit will fall out of the building. Such potentially catastrophic failure of the sealant is typically hard to detect, unless the elements are observed leaking around the glass unit. Moreover, the seeds for sealant failure can be initially sown if the building is not properly surfaced for good adhesion, which can be difficult to accomplish and inspect in the field. Four sided silicone systems, while attractive to the industry, have nevertheless found disfavor for these reasons.